Adjustment

The valves should be adjusted with the engine running at idle and at normal operating temperature.

Start the engine and allow it to warm to normal operating temperature. Make sure that the engine idles down to normal curb idle. With manual transmissions, the transmission should be in Neutral. With automatic transmissions, the transmission should be in Drive, with the parking brake set and the wheels blocked.

Using a flat feeler gauge, pass the gauge between the rocker arm and the top of the valve stem. A slight drag should be felt. See the accompanying illustration for valve identification. The valve clearances should be:

1967-75 Models

Intake: 0.012 in. (0.30mm)

Exhaust: 0.024 in. (0.2mm)

1976-80 Models

Intake: 0.010 in. (0.25mm)

Exhaust: 0.020 in. (0.50mm)

Fig. Fig. 1: Valve location for common 6-cylinder engine

If clearance is not as specified, turn the adjusting screw on the end of the rocker arm to adjust it. We recommend a socket and ratchet with a long extension for this job.

When all valves are adjusted, shut off the engine, wipe up the mess and install the valve cover, using a new gasket coated with sealer.

6-251 Engine

The valves should be adjusted with the engine running at idle and at normal operating temperature.

Start the engine and allow it to warm to normal operating temperature. Make sure that the engine idles down to normal curb idle.

Remove the valve side cover.

Using a flat feeler gauge, pass the gauge between the tappet and the valve stem. A slight drag should be felt. See the accompanying illustration for valve identification. The valve clearances should be:

Intake: 0.010 in. (0.25mm)

Exhaust: 0.014 in. (0.35mm)

If clearance is not as specified, turn the adjusting screw on the end of the tappet to adjust it. If the engine is to be operated under abnormal conditions, such as extreme heat or continuous high speeds, an additional 0.002 in. (0.05mm) clearance is recommended for both intake and exhaust valves.

When all valves are adjusted, shut off the engine, wipe up the mess and install the valve cover, using a new gasket coated with sealer.

Diesel Engine

See Figure 2

Valve adjustment is required on the diesel engine every 36,000 miles (57,971 km).

WARNING

Do not set the valve lash closer than specified in an attempt to quiet the lifters. This will only result in burned valves.

The engine must be cold for this adjustment. Mark the crankshaft pulley into three equal 120° sections, starting at TDC or the
0
mark.

Remove the valve cover.

Disconnect the fuel line from the injector at cylinder No. 1. Be very careful not to kink the line.

Using a socket and a breaker bar on the crankshaft bolt, turn the engine in the same direction as it normally runs, until the
0
mark on the crankshaft damper rear face is aligned with the pointer on the bottom of the timing gear case. As you are turning, keep an eye on the fuel line that was disconnected. Fuel will squirt out of the line a few degrees before you reach the
0
mark. If it doesn't squirt out, you've got the wrong piston at TDC. Turn the engine another 32° (one revolution) and you will have the No. 1 piston at TDC.

The cylinders are numbered from front to rear. Refer to the illustration for valve identification.

Fig. Fig. 2: Diesel valve arrangement

Valve lash is measured between the rocker arm and the end of the valve. To check the lash, insert a 0.012 in. (0.30mm) feeler gauge between the rocker arm and the valve. Adjust the proper clearance by loosening the locknut on the rocker arm and turning the adjusting screw. After the adjustment is made, tighten the locknut and recheck the clearance to be sure it did not change as the locknut was being tightened.

After both valves for the No. 1 cylinder are adjusted, turn the engine so that the pulley turns 120° in the normal direction of rotation (clockwise). The distributor rotor will turn 2°, since it turns at half engine speed.

Check that the rocker arms are free and adjust the valves for the next cylinder in the firing order (the firing order is 1-5-3-6-2-4). Intake and exhaust valves should have the same clearance of 0.012 in. (0.30mm).

Turn the engine 120° to adjust each of the remaining cylinders in the firing order. When you are done, the crankshaft will have made two complete revolutions (720°).

Install the rocker cover with a new gasket, then attach the fuel line to the injector. Start the engine and check for leaks.